1. Field of the Invention
The present invention relates to a head arm supporting and opening mechanism in a double-side type magnetic disk device which magnetically records signals on both sides of a flexible magnetic disk, and, more particularly, to an opening mechanism which will accommodate a hard case disk.
2. Description of the Prior Art
A conventional head arm supporting mechanism in a double-sided type magnetic disk device is shown in FIG. 1. A flexible disk 1 spins between a first magnetic head 2 and a second magnetic head 3. A carriage 4 holds the second magnetic head 3 while an arm 5 holds the first magnetic head 2. The arm 5 is held by a leaf spring 6 secured to the carriage 4 where the leaf spring 6 provides a fulcrum point for swinging the arm 5. A bracket 7 and screw 9 secure the leaf spring 6 to the carriage 4 and determines the fulcrum and bending force for the arm 5. An arm pressurizing spring 8 exerts a closing force on the arm 5. A lift member 5a is provided on the arm 5 and is connected to an arm operating plate 10 held on a bridge integral with a door handle (not shown) which is moved when the flexible disk is inserted.
When the flexible disk 1, in a flexible, thin, protective jacket 11, is inserted into the device to a position where it can be subjected to writing or reading, the first magnetic head 2 is lifted as shown in FIG. 2 to prevent interference with the disk 1 as it is being inserted. The arm operating plate 10 raises the lift member 5a provided on the arm 5 so that the arm 5 is swung about the fulcrum provided by the secured end of the leaf spring 6.
Whenever the flexible disk 1 is fixed in the conventional flexible thin protective jacket 11, the head arm supporting mechanism of FIG. 1 is sufficient. However, when the flexible disk 1 is mounted in a protective jacket or hard case 12, as illustrated in FIG. 3, which is more rigid than the material of the conventional protective jacket 11, the magnetic disk device is structured as illustrated by FIG. 4. Flexible disk 1 positioning pins 14 and 15 on spindle 13 are used to position the flexible disk 1 and to transmit rotation to the disk 1. Protrusions 16c and 16d on hard case positioning pins 16a and 16b are used to position the hard case in the X and Y directions. Steps 17a and 17b and steps 16e and 16f position the hard case in the Z direction. The hard case 12 has positioning pin holes 18, 19, 20 and 21, respectively, for the above-described positioning pins, as illustrated in FIG. 3.
When the hard case 12 is inserted into the device, it is necessary to move the hard case 12 vertically to position it at the reading and writing position. During insertion, the hard case 12 is held at an insertion level H.sub.1 (FIG. 4) by a guide (not shown), and is then moved in the direction of the arrow Y to a predetermined position. The hard case 12, together with the guide, is then moved in the direction of the arrow Z and positioned at an operating level H.sub.2 resting against steps 17a, 17b, 16e and 16f.
When the hard case is moved as described above, the first magnetic head 2 should have an opening stroke or distance of t+(H.sub.1 -H.sub.2), where t is the thickness of the hard case 12. To prevent interference between the first magnetic head 2 and the hard case 12, the opening stroke of the first magnetic head 2 is necessarily larger than the stroke necessary for a flexible case disk 1.
The conventional arm supporting system when applied to the hard case 12 suffers from several problems.
First, the leaf spring 6 provides the fulcrum for arm swing and if the opening distance of the arm 5 is increased, it is difficult to keep the mechanical strength of the leaf spring from changing due to the stress applied to the fulcrum when the arm 5 is repeatedly opened and closed. This fulcrum limitation thereby limits the opening stroke of the arm. The leaf spring 6 can be designed by utilizing the general formula for a cantilever in accordance with the equation (1): ##EQU1## where D is the leaf spring's defection, L is the length of the leaf spring 6, H is the thickness of the leaf spring 6, A is the stress on the leaf spring 6, and E is the spring constant. If it is assumed that A is the allowable stress on the leaf spring 6 and D is the deflection of the leaf spring 6 necessary for the stroke of the arm 5, then equation 1 indicates that either the length L of the leaf spring 6 should be increased or the thickness H should be decreased. However, in practice, it is difficult to increase the length of the leaf spring 6, because of the limited space available for the device. The thickness of the spring in the conventional device is generally as small as 0.1 t and if the thickness is further decreased, the reliability of the device is reduced and it becomes difficult to operate.
Second, when it is necessary to determine whether the surface of the head, which is brought into contact with the flexible disk 1, is smudged or scratched, during normal maintenance of the assembled device or when the output system is out of order it is difficult to observe the surface of the first magnetic head 2 because of the limited travel of the arm 5. In this situation, if the arm 5 is forcibly raised, the leaf spring 6 will be permanently deformed, and can no longer be used.
Third, when the arm 5 is raised by the arm operating plate 10, the leaf spring 6 can be twisted which results in the first magnetic head being permanently angled as indicated by the solid lines in FIG. 5. As a result, the first magnetic head 2 cannot be satisfactorily opened and interference between the hard case 12 and the first magnetic head 2 can occur. The angling of the head 2 due to a twisting moment occurs because of the difference in position between the lift member 5a of the arm 5 and the arm pressurizing spring 8. This problem may be eliminated by changing the position of the arm pressurizing spring 8 to the position of the lift member 5a. However, if this method is employed, then the load is applied to the first and second magnetic heads 2 and 3 in a deflected manner and the heads cannot correctly contact the flexible disk 1 and it is difficult to obtain correct outputs from the disk 1. Therefore, this correction method is not practical. If the trouble is eliminated by employing two lift members (5a) on both sides of the first magnetic head 2, the efficiency associated with assembling the device is reduced.